Thank you!

The entire thing is just knit except for the hexagon pattern, which are knit on the right (front) side, then purled on the wrong (back) side. The angled parts are made with right and left twists, which are simpler to execute than the instructions make them sound.

Colour changes are generally fairly easy. If you're thinking about doing just the hexagons in a different colour, the instructions for intarsia cables would be the best place to start. Intarsia also looks more complicated than it is in practice, though in this case I think it would be a good idea to make a practice swatch to test it first. You'd want to add the new colour when you do the first purl stitches for each hexagon on the wrong side, then I think the "2tog" part of each twist would use that strand instead of the background colour. I'd also test doing the entire twist in the second colour to see what that ends up looking like and go with whichever one I liked best.

ETA: I'd also recommend using something like a German twisted cast on and Icelandic bind off. They're both a bit stretchy, so the top and bottom of the blanket won't feel tight or pull in.